Discrimination of Forensic Soil Samples Using Variable-Number Tandem Repeat Typing of Bacillus cereus

Abstract

Soil is one of the most important physical evidence in criminal investigations, which provides useful information regarding with the relations between suspects, victims and crime scenes. Forensic soil samples are conventionally discriminated based on physical properties, such as color and mineral examinations. It is considered that molecular analysis of DNA of soil bacteria can contribute to the criminal investigation substantially, because improvement of discrimination ability of soil will be achieved by addition of biological analysis. This report describes the application of molecular analysis, which is used for discrimination of pathogens in epidemiological investigations, to forensic soil samples. Samples were taken from three sites (A, B and C), and sites B and C, which were 300 m apart, were located about 42 km from site A. Discrimination of soil samples by color and X-ray diffraction analyses were difficult. Then, Bacillus cereus was isolated from the small amount of soil samples which were as little as the lowest quantity required by the conventional method, and discriminated by variable-number tandem repeat (VNTR). The result showed that two VNTR types isolated from A were not included among isolates from B and C even 2 years later. These results suggested that the VNTR analysis using Bacillus cereus might be useful for the discrimination of forensic soil sample analysis. However, Bacillus cereus isolate shows a diversity even isolated from the same soil, therefore further data collection is required to evaluate this method for forensic soil identification.